This invention relates to a system for and method of isolating tissue for the treatment of cardiac arrhythmia, and in particular to a system and method of magnetically assisted pulmonary vein isolation.
The heart includes a number of pathways that are responsible for the propagation of signals necessary to produce continuous, synchronized contractions. Each contraction cycle begins in the right atrium where a sinoatrial node initiates an electrical impulse. This electrical impulse then spreads across the right atrium to the left atrium, stimulating the atria to contract. The impulse continues from the atria to the ventricles by passing through the atrioventricular (AV) node or junction, which acts as an electrical gateway to the ventricles. The AV junction delays the signal to the ventricles, so the atria can relax before the ventricles contract.
Disturbances in the heart's electrical system may lead to various rhythmic problems that can cause the heart to beat irregularly. Irregular heart beats, or arrhythmia, are caused by physiological or pathological disturbances in the discharge of electrical impulses from the sinoatrial node, in the transmission of the signal through the heart tissue, or spontaneous, unexpected electrical signals generated within the heart. One type of arrhythmia is tachycardia, which is an abnormal rapidity of heart action. There are several different forms of atrial tachycardia, including atrial fibrillation and atrial flutter. With atrial fibrillation, instead of a single beat, numerous electrical impulses are generated by depolarizing tissue at one or more locations in the atria (or possibly other locations). These unexpected electrical impulses produce irregular, often rapid heartbeats in the atrial muscles and ventricles. Patients experiencing atrial fibrillation may suffer from fatigue, dizziness and even stroke. In fact, atrial fibrillation can increase the risk of stroke by up to five times.
The cause of atrial fibrillation, and in particular the depolarizing tissue causing “extra” electrical signals, is currently under investigation. The undesired electrical impulses often originate in the left atrial region of the heart. Studies suggest that nearly 90% of these “focal triggers” or electrical impulses are generated within and around one (or more) of the four pulmonary veins (PV) which enter from the left atrium. In this regard, as the heart develops from an embryonic stages, left atrial conductive muscle tissue my grow or extend a short distance into one or more of the PVs. It has been postulated that this tissue may spontaneously depolarize, resulting in an unexpected electrical impulse(s) propagating in to the left atrium, and long the various electrical pathways of the heart.
A variety of different atrial fibrillation treatment techniques are available, including drugs, surgery, implants, and catheter ablation. Drugs typically only mask the symptoms and do not cure the underlying cause. Implantable devices usually correct an arrhythmia only after it occurs (and are better suited for bradycardia than tachycardia). Surgical and catheter-based treatments, in contrast, will have the potential to actually cure the problem by ablating the abnormal tissue or accessory pathway responsible for the atrial fibrillation. Catheter-based treatments rely on the application of various destructive energy sources to the target tissue, including electrical energy, radio frequency electrical energy, laser energy, cryocooling, and the like. The energy source, such as an ablating RF electrode, is normally disposed along a distal portion of a catheter.
Most ablation catheter techniques employed to treat atrial fibrillation focus on locating the ablating electrode, or a series of ablating electrodes, along extended target sections of the left atrial wall. Because the atrium wall, and thus the targeted site(s), is relatively tortuous, the resulting catheter design includes multiple curves, bends, extensions, etc. In response to recent studies indicating that the unexpected electrical impulses are generated within a PV, efforts have been made to ablate tissue within the PV itself. However, ablation of tissue in the PV itself may cause the PV to shrink or constrict. Because PV's have a relatively small diameter, a stenosis may result. An occluded PV results in the loss of up to one quarter of the lungs function as there is no redundant blood path. Even further, other vital bodily structures are directly adjacent each PV. These structures may be undesirably damaged when ablating within a PV, such as the frenic nerve which controls the diaphragm.
As a result, it is desirable to form a continuous ablation lesion pattern in the left atrium wall about the ostium of the particular PV, to electrically isolate the PV from the left atrium. As a result, any undesired electrical impulse generated within the PV could not propagate into the left atrium, thereby eliminating unexpected atria contraction. However, while PV isolation via a continuous ablation lesion pattern about the PV ostium appears highly viable, it can be difficult to achieve. It is difficult to form the necessary continuous line of ablation with conventional EP catheters. Some devices have been developed to facilitate PV isolation, including those disclosed in U.S. Pat. No. 6,325,797, for Ablation Catheter And Method For Isolating A Pulmonary Vein; U.S. Pat. No. 6,314,963, for Method Of Ablating Tissue From An Epicardial Location; U.S. Pat. No. 6,314,962, for Method Of Ablating Tissue Around The Pulmonary Veins; U.S. Pat. No. 6,311,692, for Apparatus And Method For Diagnosis And Therapy Of Electrophysiological Disease; and U.S. Pat. No. 6,237,605, for Methods Of Epicardial Ablation; U.S. Pat. No. 6,161,543, for Methods Of Epicardial Ablation For Creating A Lesion Around The Pulmonary Veins, the disclosures of which are incorporated herein by reference, but it is still difficult to perform a PV isolation procedure.
A related concern entails mapping of a PV prior to ablation. In cases of atrial fibrillation, it is desirable to identify the origination point of the undesired electrical impulses prior to ablation. Thus, it must first be determined if the electrical impulse originates within one or more PVs. However the foci that cause atrial fibrillation do not always fire when the patient is on the table, in spite of drugs and other maneuvers to induce them. One way to address this is focus-based ablation, where no ablation is made unless firing is observed in a particular part of a PV. A second way of addressing this is functional isolation. It turns out than there are directional conductive muscle fibers that enter the left atrium. These are unevenly distributed about the ostium of a given pulmonary vein such that, as one traverses the circumference of the PV, some sites will conduct and some will not. In functional isolation, only those sections of the PV circumference that conduct are ablated (although the determination of these sections is imprecise). A third way to address this is to do complete anatomical isolation of the PV; making an ablation circle all the way around rather than only ablate active pathways into a PV.
Thus two of the method require identification of the depolarizing tissue. Once the depolarizing tissue has been identified, necessary ablation steps can be taken. Mapping is normally accomplished by placing one or more mapping electrodes into contact with the tissue in question. In order to map tissue within a PV, therefore, a relatively straight catheter section maintaining two or more mapping electrodes must be extended axially within the PV. Ablation catheters configured to slide along the atrial wall cannot include a separate, distal extension for placement within the PV. Instead, an entirely separate mapping catheter must be provided and then removed for subsequent replacement with the ablation catheter. Obviously, these additional steps greatly increase the overall time required to complete the procedure.
Electrical isolation of a pulmonary vein via an ablation lesion pattern surrounding the pulmonary vein ostium presents a potentially revolutionary technique for treatment of atrial fibrillation. However, the unique anatomical characteristics of a pulmonary vein and left atrium render currently available ablation catheters minimally useful. Therefore, a substantial need exists for an ablation catheter designed for consistent positioning of one or more ablation electrodes about a pulmonary vein ostium, as well as for providing pulmonary vein mapping information.
Currently there are two techniques in clinical use for PV isolation. These are “Lasso catheter” based and “Circumferential ablation balloon” based.
In the first method, two punctures are made in the septal wall, through which two catheters are introduced into the left atrium from the right atrium. The first is an standard ablation catheter. The second is a circular mapping catheter (e.g., a Lasso catheter). The circular catheter has a small loop at the tip with a number of electrodes on the loop. The Lasso catheter is first navigated to a pulmonary vein and positioned within the ostium. The ablation catheter is then navigated to sites near the loop part of the mapping catheter (often guided by the signals emanating from various electrodes in the loop catheter). The lasso catheter provides both electrical and anatomic targeting information for the ablation catheter. Using this information, a number of ablations are made, until the physician is satisfied that the PV is indeed isolated. The procedure may then be repeated for one or more of the other pulmonary veins. This procedure requires a double trans-septal puncture. It is often hard to know exactly where the lasso catheter has been positioned, relative to the ostium of the pulmonary veins.
This procedure requires a double transeptal puncture is required. Many physicians are untrained and/or uncomfortable with this technique, and it adds time to the procedure. More specifically, the navigation is time consuming navigation (must go from the trans-septal puncture to a particular site on a Lasso catheter multiple times). There can also be difficulties in getting the catheter to the desired location. Lesions made within the PV can contribute to PV stenosis or phrenic nerve damage. It is hard to position the catheter just outside the ostium. Foci often do not present themselves during the case, and as many as 50% of PV AF foci reside at or outside the PV's, and are not treated by blocking the signal more distal (i.e., within the PV). Each of these problems is addressed by various embodiments of this invention.
In the second technique, a single puncture is made in the atrial septal wall and a specialized catheter is advanced into the left atrium from the right atrium. (could ref Atrionix and Daig devices) The device is navigated to a pulmonary vein. A balloon at the tip of the catheter is expanded with saline and the expanding balloon anchors the device within the PV. A transducer (e.g. ultrasound) is then used to transmit energy circumferentially through the saline in the balloon, to completely isolate a PV in a single application of energy. The potential advantages are complete anatomic isolation and the quickness of the procedure.
Possible problems with this technique include the fact that PV's can be non-circular with highly variable transitions from the vein to the ostium to the chamber, and a circular balloon is not always a good fit with the anatomy, or cannot be positioned perpendicular to the ostium, which can result is in ineffective lesions. The technique often ablates within the pulmonary veins, with the risk of PV stenosis. The technique requires a transeptal puncture. The technique can miss foci that are at or just outside the ostium. Also, with this technique, these devices must be navigated manually, at the bedside with radiation and lead burden. Each of these problems is addressed by various embodiments of this invention.